Mrs. Wang was indeed lying in her room resting, just as Han Lin had said, but it wasn't because she was feeling physically unwell, rather, she was emotionally distressed, feeling guilty and nervous, afraid that others might suspect her, so she simply hid in her room.
Mrs. Wang was also feeling stifled. Hurting her mother-in-law wasn't her intention at all. She had carefully planned everything. At that time, no one was home, and once her elder brother took the items and left, everyone would assume a thief had broken into the home. No one would suspect him, and even if they did, there would be no evidence to hold against her brother.